Food Allergy Basics

Adverse reactions to food are common. These reactions range from mild to severe, and they may result from any number of factors, including a true allergy to specific foods or food additives.

Here is some general information about food allergy, how to recognize symptoms, and steps you can take to manage an allergic reaction. We hope that this material helps you better understand the nature of food allergy. Please keep in mind that this information is not meant to take the place of medical advice from your own physician.

When 54-year-old Jeanette was a girl who lived in a region famous for its seafood, she regularly ate shellfish and fresh fish. After she moved inland, she found she rarely ate her favorite foods since no one fixed them the way she liked them. On a recent trip back home, she indulged in her shrimp dish—only to experience a sudden tightening of her throat, itching inside her ears, blotching on her face, and an overall feeling of “strangeness.” The emergency department physician told her it’s not uncommon for people to develop an allergy to foods they’ve often eaten before without any problems. She was advised not to eat shrimp, shellfish, or anything containing these foods again.

What is an allergy?

An allergy is the overreaction of the immune system to a substance found in our everyday environment that does not generally produce harmful effects in a majority of people. These substances are referred to as allergens.

When people have an allergy, their bodies form antibodies to fight against these allergens, which the body views as “foreign invaders.” A person can come into contact, an allergen, by breathing; eating or drinking; touching; coming near or having them injected into his or her body.

What is a food allergy?

People can be allergic to specific foods. Most people have an allergy to only one food, while some are allergic to a few foods. It is rare to have true allergy to many foods. It’s important to keep in mind that if you have an allergy to a particular food, you need to be aware of various ways that food may be used in combination with other foods.

For example, components of cow’s milk are used in preparing thousands of foods, which you might not think of as dairy products. If you are allergic to milk, you’ll want to be sure to read food labels to look for ingredients that indicate milk components were used in preparing the product.

Did you know . . . Most individuals that have had a reaction ate a food that they thought was safe?

Peanuts lead the pack for triggering severe allergic reactions. Fish and shellfish (such as shrimp), eggs, and tree nuts (like pecans or walnuts) also are known especially to cause severe reactions.

Is lactose intolerance the same as a food allergy?

Lactose intolerance is different than food allergy. It is a deficiency of the enzyme lactase and is not related to the immune system. Milk allergy is due to an interaction between an antibody (protein made by the body) and a foreign protein (e.g. cow’s milk protein).

Who gets a food allergy?

Approximately 11 million Americans—about one in twenty-five people—have known food allergies. Physicians believe that number may be steadily increasing. More than three million children in the United States have food allergies. In some cases, children may “outgrow” their allergies in their teen years.

Children with a family history of allergy and therefore a genetic predisposition to allergy may be more likely to develop food allergy. This is an area of very active research.

Keep in mind . . . You can experience a sudden allergy to a food even though you may have eaten it for years without any problems.

What are symptoms of a food allergy?

People with food allergies react in different ways. Common symptoms include the following experiences:

An allergic response to a food can occur unexpectedly and rapidly. In other cases, people may at first have only minor symptoms that, may or may not, evolve at some point to a more serious kind of reaction.

How is a food allergy diagnosed?

If your physician suspects you have a food allergy, the first step is to review your medical history and have a physical exam. Specialized tests can be done to confirm that you are allergic to certain foods. The following types of tests are commonly performed to determine what allergens are causing the allergic response.

Skin test. A tiny drop of extract of the allergen is placed onto the skin. A red, itchy, raised area around the site indicates a positive reaction. However, a positive skin test is not considered to be a 100% accurate diagnosis, although it does help support a food allergy diagnosis. In fact, many people regularly eat foods that don’t cause an allergic reaction, even though in a skin test the result is positive. A negative skin test does not completely rule out the possibility that allergy is the problem. However, negative skin tests in all individuals except infants, for the major foods, are very useful for ruling out food allergy and deciding who will be challenged to the food. Skin tests for fruits and vegetables are often performed with fresh foods.

Radioallergosorbent test (RAST). This approach tests your blood for antibodies to specific foods. Although more costly and less sensitive than skin testing, RAST is particularly useful when eczema and other skin conditions make skin testing difficult.

Oral food challenge. In this test, you eat select foods to see which ones cause an allergic response. An oral challenge test carries the risk of causing an allergic reaction, so the test should be done with a physician present and in a setting where allergic reactions can be treated promptly. Oral challenges provide the best results for determining food allergies.

Elimination diet. Used when other tests provide unclear results, this diet requires that you keep a detailed record of everything you eat and drink for several weeks. Then, foods suspected of causing the reaction are removed from your diet, making sure that the suspected foods are not present in anything you consume. You continue to keep a record of your reactions to foods as they are eliminated from your diet. In this way, your physician may be able to help you determine what food(s) is the cause of your allergic response. Alternatively, one may keep a log of symptoms while consuming a normal diet and then go on a very strict diet of few foods and see if the symptoms change. If they do not, then a food allergy is very unlikely. If they do, then further investigation should be undertaken.

NOTE: It is very important not to rely on skin prick or RAST tests only for a diagnosis and you should not remove foods from the diet without a physician’s direction.

Masqueraders of food allergy?

Several factors can make diagnosis of a food allergy difficult.

• The allergic reaction may depend on the amount of food consumed, the presence of other foods that can slow digestion, or medications, such as antihistamines, that may hide reactions.

• Proteins—the antigens within the food or drink that trigger allergy—may be altered in some way by cooking or processing. In fruits or vegetables, for example, some antigens are present only at a particular stage of ripeness. However, almost all food allergens that cause severe reactions are not easily changed by cooking. Those that cause pollen-food allergy syndrome or oral allergy syndrome are more labile and can be altered and made non-allergenic by cooking.

• Reactions apparently related to presence of a food or food additive may, in reality, be due to another food that was accidentally added during preparation.

• Toxins and food poisoning can cause reactions that may be confused with symptoms of food allergy.

• Some foods upset the stomach and resemble food allergy.

• Certain medical conditions, such as a hiatal hernia, stomach ulcers, or diverticulosis are associated with acute symptoms after eating and may be confused with a food allergy.

What can be done to avoid developing food allergies?

It is strongly recommended that all infants be breast fed for 4-6 months.

Are there ways to prevent an allergic reaction if you have a food allergy?

Yes. Here are some suggestions to follow as you plan your meals, outings, and travel.

• Do not consume foods that cause a reaction. It seems like an obvious thing to do, but it is not always as easy as it sounds. Many packaged or processed foods contain hidden ingredients, or very small amounts of food additives derived from foods, which commonly trigger allergies. And there may often be the temptation to try “just a little bit” of a food known to cause an allergy. People with a severe allergy can develop anaphylactic shock from trace amounts of the food to which they are allergic. Many patients with food allergy may benefit from the help of a skilled dietitian. There is also excellent information on the website of the Food Allergy and Anaphylaxis Network.

• Read the ingredients lists on all food labels. Make sure allergy-causing foods are not included. Watch for use of substances made from, or derived from, the food that causes the allergy (e.g. milk proteins: casein and whey; egg proteins: ovalbumin, ovomucoid). Read the list even if you have used the product before because ingredients can change! Avoidance of the allergy causing food is critical, that means reading ingredient labels all the time for all foods.

• Arrange for special foods when traveling. Stay in hotels with kitchenettes so you can prepare your own food as necessary. Order airline meals in advance. Let your hosts know of special dietary considerations.

• Talk to restaurant staff about your needs. Ask about ingredients in food and how it is prepared, including what other foods are cooked near or with the food you want to order.

• Discuss infant formula options with your physician. Elemental formulas or formulas with altered protein should prevent food reactions. Talk with your child’s pediatrician about other formula options. Do not assume products labeled “hypoallergenic” will not cause a reaction.

What is the treatment when a food allergy reaction does occur?

When a food allergy reaction is severe, follow the written instructions provided by your physician. Epinephrine is the medication of choice for a severe reaction. If prescribed, always carry it with you. Epinephrine is available, EpiPen® or Twinject®. If epinephrine is used, you must seek professional medical attention and be transported to the nearest hospital for additional treatment and observation. Symptoms may recur within minutes to a few hours.

If you have life-threatening food allergies, you should wear a Medic Alert bracelet or necklace to let health care workers know of your allergy in case of an emergency.

Who should treat food allergies?

Many patients are treated for allergies of all kinds by their pediatrician, internist, or family physician. However, if your allergy symptoms are not under control within 3-6 months, or if you have severe persistent allergies, or if you are having allergy symptoms that require emergency treatment, it may be time to see an allergist. Allergists/Immunologists are specialists who treat allergies. Those who have completed training in those specialties are usually called board-certified or board-eligible.

Does health insurance cover treatment for food allergies?

Most health insurance plans provide some level of coverage for food allergy patients. Check with your insurance carrier for details. Some things you may want to find out might include:

• Do you need a referral to an allergy care specialist from your internist, family physician, or pediatrician?